Albion continued their charge towards the top of the table with a fourth win in a row.
Goals in each half by captain Paul Rogers and defender Kerry Mayo stretched the rampant Seagulls' unbeaten run to seven matches.
It was by no means a classic on a boggy pitch, but Micky Adams' men were worthy winners on the strength of a dominant display after the break.
A record Withdean crowd of 6,731 saw Rogers bring an uneventful opening period to life in the 42nd minute.
He headed his second goal in four games and second in successive seasons against Orient from a Paul Watson cross.
Carl Griffiths struck a post for the visitors two minutes later, but it was all Albion in the second half.
Mayo calmly side-footed his first goal of the campaign from just inside the box on 64 minutes to complete a hat-trick of home victories for his side.
Keeper Mark Cartwright suffered an injury in the later stages, which prevented him from taking goal kicks.
His fourth clean sheet in a row never came under serious threat after Griffiths' near miss.
Albion have now moved three points above Orient and Adams is on course for the Third Division manager of the month award.
Today's triumph was the Seagulls' fifth in the League in September, which has also included draws at promotion favourites Cardiff and Second Division Millwall in the Worthington Cup.
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